I think the Maggies are intrinsically limited in their bass output by their very nature, so I don't think the 1.7s will be able to stretch much lower.

I built a pair of dipole woofers (each with 2 12" sub drivers) and a custom active crossover from John at musicanddesign.com to go with my 1.6s, and now they truly are large. Flat response all the way down to 25 Hz. Then two big subs to get the last 8Hz or so below that. You are definitely missing some stuff in The Dark Knight.

But for music, I usually just bypass bass management and don't use the subs.

How come you aren't running any kind of low end augmentation for yours, out of curiosity?